Accurately forecasting binary tropical cyclone (TC) interactions remains a critical challenge in operational numerical weather prediction. A major limitation is that existing identification criteria rely on empirical distance thresholds which are susceptible to large-scale environmental steering. To overcome this limitation, we propose 3D-VISCOUS, a physically constrained and objective criterion rooted in the three-dimensional baroclinic structure of TCs. Under this framework, a Dominant TC (DTC) must generate sufficient vertical wind shear (VWS) to induce a wavenumber-1 convective asymmetry in the Affected TC (ATC).
Based on criterion above, the identified interacting TC samples in the western North Pacific (WNP) and North Atlantic (NA) during 1981–2020 show two previously obscured features. First, attributed to the distance-dependent reversal of the net steering effect from vertical structure of DTC, the interacting TCs exhibit tendency to cyclonically approach each other within critical distance(1500-1800 km) but to anticyclonically escape beyond this distance. The critical distance was naturally highlighted without any subjective distance threshold input. Second, DTC modulates the thermodynamic environment surrounding the ATC, suppressing rapid intensity changes of ATCs reaching severe typhoon in both basins. In WNP, this effect even decouples the intensity change of ATCs from the VWS. Critically, evaluations of global numerical weather prediction model forecasts show that the rotation rates of interacting TCs are systematically underestimated, highlighting the need for improved depictions of three-dimensional TC interactions. These results establish 3D-VISCOUS as a powerful diagnostic for both understanding binary TC dynamics and exposing critical weaknesses in current prediction systems, with direct implications for improving tropical cyclone forecasts in a changing climate.
 

Binary Tropical Cyclone Interaction,Tropical Cyclone Convective Structure,Vertical Wind Shear